Overview
ISO 14934-3:2012 - "Fire tests - Calibration and use of heat flux meters - Part 3: Secondary calibration method" specifies standardized methods for the secondary (transfer) calibration of heat flux meters used in fire testing. The standard applies only to instruments with plane receivers (not wire, spherical or other non‑planar receivers) and defines how to compare a working-standard heat flux meter against a secondary-standard meter whose sensitivity has been established by a primary method.
Keywords: ISO 14934-3, heat flux meter calibration, secondary calibration method, fire tests, radiant heat flux, transfer calibration
Key topics and technical requirements
- Scope and principle: Transfer calibration is performed by comparing outputs of the working-standard and a secondary-standard heat flux meter at different irradiance levels.
- Irradiance levels: Calibrations are conducted at a minimum of 10 different levels of irradiance, obtained by varying radiant-source temperature or source-to-sensor distance.
- Radiant source: Electrically powered radiant sources (spherical, flat or conical) are used; the source must be larger than the meter sensing surface and maintained at a preset, constant temperature during measurements.
- Mounting arrangements: Two main setups - vary the temperature of the radiant source or vary the distance between source and meter. Mounts must position the meter centrally beneath the source and avoid convective airflows and hot masses.
- Instrument matching: The secondary-standard meter should be the same type and range as the working-standard (e.g., Schmidt‑Boelter type), with identical outer diameter and water-pipe orientation where practical; differing diameters require uncertainty analysis.
- Recording and data: Recording instrumentation must log readings at intervals not longer than 5 s and have appropriate ranges; using the same recorder for both meters is recommended.
- Environment controls: Calibration must be carried out in a stable, low-draught environment (airflow ≤ 0.2 m/s) with surrounding surfaces kept below 40 °C to limit background radiation.
- Supporting guidance: Annexes cover accuracy of calibration, care of meters, practical guidance and inter-laboratory maintenance procedures.
Applications and who uses it
- Fire test laboratories that maintain working-standard heat flux meters for tests where specified irradiance is critical (e.g., material flammability, reaction‑to‑fire tests).
- Calibration labs performing transfer calibrations to ensure consistent irradiance measurements across test equipment.
- Quality managers, test engineers and accreditation bodies ensuring traceability of radiant heat flux measurements in standards-based fire testing.
Related standards
- ISO 14934-1 - General principles for heat flux meter calibration
- ISO 14934-2 - Primary calibration methods (required for secondary-standard traceability)
- ISO 14934-4 - Guidance on use in fire tests (Technical Specification)
- ISO 5660-1 and test method standards referenced for cone heater arrangements
Using ISO 14934-3 helps ensure accurate, traceable measurement of radiant heat flux in fire testing, improving comparability and reliability of test results.